(1) Field of the Invention
The present invention relates to a usage parameter control (UPC) circuit for controlling a flow amount of cells based on reference threshold information relating to cell traffic.
As a basic technology for a Broadband Aspects of Integrated Services Digital Network (B-ISDN), an Asynchronous Transfer Mode (ATM) technology for asynchronously transferring cells has been developed. In the ATM network, the amount of cell flow is controlled based on traffic parameters declared by subscribers. This control is called policing control or a Usage Parameter Control (UPC) which is an essential technology for smooth operation of the ATM network. The user declaration traffic parameters, however, are different depending on the subscribers. This difference makes it difficult to realize a UPC circuit.
(2) Description of the Related Art
As a conventional policing control method, a time interval method has been proposed in which the cell transmission is controlled by counting cell arrival time intervals for respective cells and by comparing each time interval with a reference threshold time.
Another conventional policing method has been proposed such as a T--X method in which the number of cells arriving within a reference threshold time period are measured and the number is compared with a reference threshold value to control the cell transmission.
Still another conventional method has been proposed such as a dangerous bridge (DB) method in which the number of cells arriving during a reference threshold time are counted while the starting time point of the reference threshold time period is shifted by one cell transmission time at the time of each counting operation, and the counted number is compared with a reference threshold number of cells, to control the cell transmission.
In the time interval method, the cell arrival time interval is determined for each cell so that there is a small amount of flexibility in the continuous control of cell speed.
The T--X method has a large amount of flexibility in the continuous control of cell speed, however, when cells are concentrated at a boundary region of the reference threshold time period, these cells cannot be efficiently restricted.
In the conventional DB method, a plurality of taps in a bridge memory must be accessed each time a cell arrives. This simultaneous access of plural taps is difficult to realize because the memory access time is restricted to a certain period. In addition, there is another problem in the conventional DB method in that, if a software error is generated in a memory or in a counter, the error does not disappear within a limited time period.
Accordingly, in the conventional UPC circuit, since the parameters declared by subscribers are different depending on the subscribers, and if all of the parameters are to be taken into consideration, the conventional UPC circuit has a disadvantage of being too complex and requiring large amounts of hardware.
An object of the present invention is to provide a new UPC circuit having a simple traffic judgement unit and being superior in general purpose characteristics and flexible expandability.